This invention is an improved paperboard tray for heating, in a microwave oven, food packaged in the tray.
Food processors commonly package food, particularly frozen food, in a paperboard tray that is intended to be placed in a microwave oven to heat the food. When the tray is totally transparent to microwave energy, the peripheral edges of the food tend to overheat while the center of the food remains relatively cool. It is known that the food may be heated more uniformly by including a material opaque to microwave radiation, such as aluminum foil, in the peripheral wall of the tray. For example, British patents 1,593,523 and 2,112,257 and U.S. Pat. No. 4,351,997 disclose such trays wherein the trays are formed by pressing. However, manufacturing trays by pressing requires a substantial capital investment for tooling, which may not be economical for low volume applications. U.S. Pat. No. 4,626,641 discloses a microwave transparent tray that fits snugly into a tray made by simply folding and gluing a blank made from a laminate of paperboard and aluminum foil wherein a hole is cut in the aluminum layer to allow microwave energy to penetrate the bottom of the tray. U.S. Pat. No. 5,370,883 discloses essentially the same tray. However, the trays disclosed in these patents require two different components to manufacture. This invention provides a partially-shielded tray that is made by folding a unitary blank.